In the related art, there is proposed a delay (echo) adding technique in an audio device.
JP H10-124081 A describes a reverberation adding circuit that can obtain a superior adjustment feeling of reverberation sound and an audio device which uses the reverberation adding circuit, wherein a microphone signal from a microphone is supplied to a mixing unit, a microphone output signal which is output from the mixing unit is supplied to a delay unit to delay the signal, and the delayed signal is supplied to a reverberation sound volume adjuster. A reverberation signal which is obtained by adjusting a signal level of the signal by the adjuster is supplied to the mixing unit and mixed with the microphone signal, to produce a microphone output signal. When the reverberation sound is reduced by the adjuster, a rate of attenuation of the reverberation sound is set large and a duration of the reverberation sound is shortened. When the reverberation sound is increased, the rate of attenuation of the reverberation sound is set small, and the duration of the reverberation is elongated. A superior adjustment feeling of the reverberation sound can thus be obtained.
JP S63-006799 U discloses an echo circuit which uses a signal delay element such as a BBD (Bucket-Brigade Device), wherein an echo circuit is formed in which an input signal which is applied to a signal input terminal is input to the BBD via a first amplifier and a first low-pass filter, a delay signal which is output from the BBD is added to a direct input signal from the signal input terminal via a second low-pass filter, a second amplifier, and a high-pass filter, and a delay signal which is output from the second amplifier is fed back to an input stage of the first amplifier via an attenuator, and a cutoff frequency of the high-pass filter is set changeable, to thereby adjust the reverberation time.
Normally, addition of a delay (echo) effect can be achieved by multiplying a gain to a delayed waveform and applying a mixing process, and a preliminary filter is provided on the feedback loop so that a high range of the delayed sound is attenuated. The digital signal process can be achieved by repeating a recording process of the input digital signal in a delay memory for a period corresponding to a delay time period and a reading process of the signal from the delay memory. Because the delay time is up to a few hundred milliseconds to a few seconds, when the process is to be realized by a DSP (Digital Signal Processor), the delay unit is realized by a ring buffer of an external memory. In this manner, a memory region for storing the delay data, an address management of the delay data, and control of the reading timing of the delay data becomes necessary, which results in complication of the circuit structure. In addition, because the memory used for the delay has a large number of samples, an external memory is in many cases required, which may cause an increase in the cost.